The present invention concerns a semiconductor device and a production process thereof, as well as a wire bonding device used therefor. More specifically, the present invention relates to an improvement for the bondability in the wire bonding, for example, to a technique useful when applied to electrical connection between electrodes and leads of a semiconductor pellet in the production steps of a semiconductor device.
The production process for a semiconductor device includes a wire bonding step for the electrical connection between electrodes of a semiconductor pellet on which a semiconductor device such as IC or LSI is formed and leads. As one of the wire bonding devices used in such a step, there has been known a ball-bonding type bonding device of applying a high voltage between an electric discharge electrode and the top end of a wire held by a capillary as a wire bonding tool, causing electric discharge to make the top end of the wire spherical (into a ball) and, thereafter, lowering the capillary to crush the ball therewith and press-bonding under heating, thereby connecting the wire to a body to be bonded. Further, there has also been known a wire bonding device in which the space between the top end of the wire and the discharge electrode disposed opposing thereto can be maintained as a reducing gas atmosphere.
Such a wire bonding device has been described, for example, in Japanese Patent Laid-Open No. Sho 58-169918.
In semiconductor devices such as ICs, LSIs, transistors, etc., gold (Au) wires of from 20 to 50 .mu.m diameter have often been used for at present the connection between an aluminum (Al) electrode on a silicon (Si) chip (pellet) and a lead frame. Upon connecting the wire to the silicon chip, a ball is formed to the top end of a gold wire by means of electric discharge or hydrogen flame and the ball is connected by press-bonding under heating or supersonic welding. However, if the gold Au wire is made fine for making the density higher and the size smaller in a semi-conductor device, the strength of the wire is weakened thereby causing problems of deformation or disconnection of the wire upon resin encapsulation.
In view of the above, there has been an important subject for the development of a ball bonding tenchique using other materials than gold.
Copper (Cu) and aluminum (Al) may be considered as the material for the wire, and earnest studies have been made various research organizations for using copper (Cu) wires in view of the electroconductivity and the strength, because copper wire causes neither deformation nor disconnection even when it is made finer than the gold wire.
However, it has been considered extremely difficult technically to use the copper wire since it is oxidized more easily as compared with the gold wire, making it difficult to obtain a ball of a high spherical shape, as well as the hardness of the ball is high.
Recently, copper balls of high spherical shape can be obtained by forming a ball in an inert gas containing hydrogen as disclosed in Japanese Patent Laid-Open No. Sho 58-154241 and the study for the copper ball bonding has become vigorous.
Further, attempts for increasing the purity of the copper wire has been made for decreasing the ball hardness (Japanese Patent Laid-Open Nos. Sho 60-124959, 59-13662 and 59-139662). That is, if the ball hardness is high, since there is a great possibility of damaging the silicon chip upon ball bonding, the adequate bonding region is extremely narrow as compared with the case of gold wire, making it not suitable to the mass production. However, the ball hardness is not reduced by so much even if the purity of the copper is improved, and a novel technique for reducing the ball hardness has strongly been demanded.